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5. What role does fluoride play in preventing tooth decay?

Both water fluoridation and application of fluoride directly to the teeth and gums, for example using fluoridated toothpaste or varnish, can prevent tooth decay. Fluoride is incorporated into the tooth enamel while teeth are growing, and this reduces decay later on when teeth have erupted. The preventive effect is most important for the permanent, adult teeth. There is no clear advantage of water fluoridation over direct application for prevention, and systemic exposure via drinking water is unlikely to benefit people whose teeth have already grown. Europe-wide trends show a reduction in tooth decay in 12 year-olds regardless of whether water is fluoridated or not.

Direct, topical application is the most effective way to prevent tooth decay. It keeps up fluoride levels in the mouth but does not normally raise them appreciably elsewhere.

In children, there is a very narrow margin between the beneficial effects of reducing decay and exceeding the dose which causes dental fluorosis.

There is some evidence to support the idea that population-wide administration of fluoride, by adding it to drinking water, milk or salt, can reduce social inequalities in dental health. At the moment, children from lower socio-economic groups tends to have more tooth decay, and to benefit more from water fluoridation. However, the overall weight of evidence is not enough to substantiate the idea that water fluoridation is the best way to tackle social inequalities in dental health.